Re: [PATCH -next] cgroup: fix uaf when proc_cpuset_show

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On 2024/6/25 22:16, Waiman Long wrote:
On 6/25/24 10:11, chenridong wrote:


On 2024/6/25 18:10, Michal Koutný wrote:
Hello.

On Tue, Jun 25, 2024 at 11:12:20AM GMT, chenridong<chenridong@xxxxxxxxxx>  wrote:
I am considering whether the cgroup framework has a method to fix this
issue, as other subsystems may also have the same underlying problem.
Since the root css will not be released, but the css->cgrp will be
released.
<del>First part is already done in
    d23b5c5777158 ("cgroup: Make operations on the cgroup root_list RCU safe")
second part is that</del>
you need to take RCU read lock and check for NULL, similar to
    9067d90006df0 ("cgroup: Eliminate the need for cgroup_mutex in proc_cgroup_show()")

Does that make sense to you?

A Fixes: tag would be nice, it seems at least
    a79a908fd2b08 ("cgroup: introduce cgroup namespaces")
played some role. (Here the RCU lock is not for cgroup_roots list but to
preserve the root cgrp itself css_free_rwork_fn/cgroup_destroy_root.

HTH,
Michal

Thank you, Michal, that is a good idea. Do you mean as below?

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c

index c12b9fdb22a4..2ce0542067f1 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -5051,10 +5051,17 @@ int proc_cpuset_show(struct seq_file *m, struct pid_namespace *ns,
        if (!buf)
                goto out;

+       rcu_read_lock();
+       spin_lock_irq(&css_set_lock);
        css = task_get_css(tsk, cpuset_cgrp_id);
-       retval = cgroup_path_ns(css->cgroup, buf, PATH_MAX,
- current->nsproxy->cgroup_ns);
+
+       retval = cgroup_path_ns_locked(css->cgroup, buf, PATH_MAX,
+               current->nsproxy->cgroup_ns);
        css_put(css);
+
+       spin_unlock_irq(&css_set_lock);
+       cgroup_unlock();
+
        if (retval == -E2BIG)
                retval = -ENAMETOOLONG;

        if (retval < 0)

That should work. However, I would suggest that you take task_get_css() and css_put() outside of the critical section. The task_get_css() is a while loop that may take a while to execute and you don't want run it with interrupt disabled.

Cheers,
Longman



--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -5050,11 +5050,18 @@ int proc_cpuset_show(struct seq_file *m, struct pid_namespace *ns,
        buf = kmalloc(PATH_MAX, GFP_KERNEL);
        if (!buf)
                goto out;
-
        css = task_get_css(tsk, cpuset_cgrp_id);
-       retval = cgroup_path_ns(css->cgroup, buf, PATH_MAX,
-                               current->nsproxy->cgroup_ns);
+
+       rcu_read_lock();
+       spin_lock_irq(&css_set_lock);
+
+       retval = cgroup_path_ns_locked(css->cgroup, buf, PATH_MAX,
+               current->nsproxy->cgroup_ns);
+
+       spin_unlock_irq(&css_set_lock);
+       rcu_read_unlock();
        css_put(css);
+
        if (retval == -E2BIG)
                retval = -ENAMETOOLONG;

        if (retval < 0)


Yeah, that looks good, i will test for a while. I will send a new patch if no other problem occurs.

Thank you.

Regards,
Ridong






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